Exposure of skin to ultraviolet (UV) radiation (UVR) causes sunburn, tanning, carcinogenesis, skin aging, and impaired immunity. This competitive renewal proposes to continue work on the effects of UVR on Langerhans cells (LC) and on immunity in skin. In the last five years we have: 1) characterized two prototypic long-term LC lines (XS52 and XS106), which are currently used by as many as 30 investigators worldwide, 2) determined that LC undergo "terminal" maturation during antigen- specific interaction with T cells, a mechanism by which LC accomplish their critical transition into DC specialized for the delivery of T cell stimulatory signals, 3) determined that UVR impairs the antigen presenting capacity of LC in the absence of other epidermal cells, 4) established a "dual mechanism" model of LC depletion in which down-regulated expression of CSF-1 and GM- CSF receptors and CSF-1-deficiency play roles, 5) observed that UVR at sublethal fluences induces secretion of IL-1beta, IL-6 and TNFalpha, 6) reported that UVR sensitizes XS52 LC to undergo apoptosis upon subsequent antigen-specific interaction with T cells, 7) established hydrogen peroxide as one mediator in UV- induced antigen presenting impairment, 8) reported that UVR activates selected transcription factors in keratinocytes. We have employed recently developed technology using "decoy nucleotides" to explore the role of NFkB-dependent pathways in UVR-mediated effects in skin. A double-stranded 20 bp oligonucleotide that contained a consensus sequence for NFkB- binding sites (NFkB decoy): 9) competed with the binding of a conventional 32P-labeled NFkB DNA probe to nuclear extracts prepared irradiated XS106 cells, 10) prevented UV-induced cytokine production in vitro and in vivo, and 11) prevented UV- induced inflammation in vivo. Using GeneArray technology, we: 12) identified 52 genes that were consistently up-regulated (greater than 3-fold) by UVR. In the next five years, we propose to: 1) determine the extent to which NFkB signaling pathways mediate UV-induced alterations in LC function, 2) characterize the roles of UVR-dependent NFkB activation in keratinocytes in vivo, 3) characterize the roles of UVR-dependent NFkB activation in LC during the induction of UVR-induced immunosuppression, and 4) identify UVR/NFkB "fingerprint" genes that are induced by UVR in a NfkB-dependent manner in keratinocytes and LC.